Plasma jet CVD apparatus for forming diamond films

ABSTRACT

An apparatus for depositing a diamond film on a substrate includes a first electrode formed as an enclosed body having a nozzle for jetting thermal plasma opening therefrom and a second electrode of opposite polarity positioned in the nozzle. The apparatus additionally includes a power source for applying a direct current voltage between the electrodes. A gas is fed between the electrodes as a direct current voltage is applied thereto, whereby the gas is formed into a thermal plasma which is jetted through the nozzle. A starting gas feed system is included for feeding gaseous starting compounds for vapor phase deposition to the plasma jet and a powder supplying pipe is provided for feeding a metal powder between the electrodes.

This application is a division of application number 07/790,115, filedNov. 12, 1991, now U.S. Pat. No. 5,260,106, which in turn is acontinuation of application Ser. No. 07/562,606, filed Aug. 3, 1990 nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for vapordeposition of diamond film. More, specifically, it relates to a highlyefficient method and apparatus for uniformly vapor depositing a diamondfilm having superior adhesiveness, superior hardness, and smoothnessonto a treated object or substrate and also for depositing a diamondfilm onto a carburizing material.

2. Description of the Related Art

Diamond is a allotropic form of carbon (C), which exhibits a diamondstructure, has a high Mohs hardness of 10, and has a superior thermalconductivity of 1000 or 2000 W/mK, compared with other materials.Therefore, various applications have been developed for using thesecharacteristics.

For example, because of its high hardness, diamond has been consideredfor use in connection with drill blades or bits. Attempts have been madeto cover such tools, which are made of high hardness sintered alloyssuch as tungsten carbide (WC), with a diamond film. Further, because ofits high heat conductivity, diamond has been utilized as a heat sink forLSI, VLSI, laser diode or other semiconductor devices.

When coating a diamond film on a tool made of tungsten carbide (WC) ormolybdenum carbide (MoC), even if a chemical vapor deposition apparatus(abbreviated as a "CVD" apparatus) is used similar to that shown in FIG.1 and the film is grown directly by chemical vapor deposition(abbreviated as "CVD"), the film peels off easily due to differences inthe coefficients of heat expansion.

The operation of the above-mentioned known apparatus is as follows.

An object (for example, a tool) to be treated or substrate is placed ona substrate holder 3 cooled by cooling water 2. At the top of thereaction chamber 4 is an anode 6 and a cathode 7 for forming a plasmajet 5. A starting gas 8 is supplied between the anode and the cathode. ADC power source 10 is provided connecting the anode 6 and the cathode 7.At the bottom of the reaction chamber 4 is an exhaust outlet 11. For theCVD growth of diamond, a mixed gas 8 of hydrogen (H₂) and a hydrocarbon,for example methane (CH₄), is supplied so as to flow between the anode 6and the cathode 7 and into the interior of the reaction chamber 4. Theexhaust system is operated to exhaust chamber 4 through the exhaustoutlet 11 and the inside of the reaction chamber 4 is held at a lowvacuum, in which state are arc discharge 12 is caused between the anode6 and the cathode 7, the heat of which causes decomposition andplasmatization of the starting gas 8, whereupon the plasma jet 5including carbon plasma strikes the metal plate 1 and a diamond film 13composed of fine crystals is grown on the metal plate 1. Thus, it ispossible to grow a diamond film 13 on the treated object 1, but sincethe coefficients of heat expansion differ (for example, the linearexpansion coefficient of diamond is 0.0132×10⁻⁴ K⁻¹, while that of W is0.045×10⁻⁴ K⁻¹) and since the temperature is decreased from the hightemperature of 800° C. or more at which the CVD reaction is performed toordinary temperature, the diamond film 13 easily peels off of thetreated object 1.

Therefore, in the prior art, when coating a diamond film on a tool madeof WC, for example, elements (for example of Co) included in the WC assintering reinforcements and for causing a reduction of the adhesivenesswere chemically removed, and then the CVD method was used to grow thediamond film. Alternatively, mechanical scratches were made in thesubstrate and the growth was performed over the same. However, sinceadhesiveness decreases with film thickness, the thickness of the grownfilm was limited to several μm, and even so the adhesiveness wasinsufficient for practical use. The present inventors previouslyproposed, as a method for resolving this problem, the provision of acoating material layer 15 with a coefficient of heat expansion close todiamond on the treated object 1, as shown in FIG. 2, and the growth of adiamond film 13 on the same (Japanese Unexamined Patent Publication(Kokai) No. 1-145313 published Jun. 7, 1989). However, when actuallyused, the adhesiveness provided was still not satisfactory for tool use.

As mentioned above, diamond has the highest hardness among allmaterials, so attempts have been made to use it to form drill blades andbits. However, when diamond is coated on a tool made of WC, for example,the coating easily peels off since the heat expansion coefficientsdiffer and therefore this has not been commercialized.

As mentioned earlier, since diamond has a high heat conductivity, it hasbeen considered for use as a heat sink for semiconductor devices and isbeing commercialized for this. FIG. 2A is a perspective view of acooling structure, wherein a heat sink 15 comprised of a diamond isbrazed by gold on a subcarrier 14 comprised of cooper (Cu). On top ofthis heat sink 15 is bonded a semiconductor laser or other semiconductorchip 16 by, for example, gold-tin solder.

FIG. 2B shows the sectional structure of the heat sink 15, wherein atitanium (Ti) film 18, platinum (Pt) film 19, and gold (Au) film 20 areformed in successive layers at thicknesses of about 2000 Å respectively.The reason why the Ti film 18 is used is that it forms titanium carbide(TiC) with the diamond film 17 and has a good adhesiveness. Further, thereason why the Pt film 19 is interposed is so as to correct the poorwettabilities of the Ti film 18 and Au film 20. However, such a heatsink 15 suffers considerably from the effects of the heat conductivitiesof the metal films enclosing it and from the complicated nature of thestructure. Further, the bonding of the separate layers requires hightemperature, so the semiconductor chip can easily be damaged, or thebonding requires special skills, so the price becomes high.

With reference to the apparatus of FIG. 1, when plate 1 plated on asubstrate holder 3 is cooled by cooling water 2, it becomes possible toform a diamond film 13 thereon.

As mentioned above, diamond has an extremely superior heat conductivityof 2000 W/mK, so it is being commercialized as a component material forheat sinks, but as shown in FIG. 2B, a Ti/Pt/Au metal film is formed inlayers on the diamond film. Therefore, there are the problems that theheat conductivity of the diamond is impaired and the cost becomeshigher.

Furthermore, as mentioned above, diamond is used for high performancetools utilizing its hardness, and is used as heat sinks for deviceswhere there is a large generation of heat such as laser diodes becauseit has a high heat conductivity which is several times that of copper.However, the surfaces of conventional thick diamond films have been veryrough and the use of these films has required polishing of the surfacewith a diamond disk etc. This polishing work has required considerabletime and labor. The density of nucleus production of diamond is 10⁷ to10⁹ cm⁻², a density which is much smaller than the density of othermaterials (10¹³), therefore specific crystal particles selectively growand the surface becomes very rough. In particular, this trend isstriking in the case of thick diamond films (a roughness of about 0.2 mmwith film thicknesses of 2 mm).

Furthermore, as mentioned above, attempts have been made to cover toolswith diamond to utilize its high hardness. As methods for synthesizingdiamonds, there are known the high pressure synthesis method and the lowpressure synthesis method. The high pressure synthesis method issuitable for forming relatively large sized monocrystals, but theapparatus is cumbersome and the speed of growth is very slow, so thereis the problem of a higher cost. As opposed to this, the low pressuresynthesis method includes the microwave plasma chemical vapor depositionmethod and the electron assisted chemical vapor deposition method. Thespeed of growth is much higher compared with the high pressure methodand it is possible to form diamond as fine crystals on the treatedsubstrate.

Contrary to the above, the present inventors have developed a method forchemical vapor deposition (CVD) of a diamond film using the plasma jetchemical vapor growth apparatus shown in FIG. 1, as mentioned above.However, to cause the growth of the diamond film by plasma jet CVD, acarbon source such as CH₄ or other hydrocarbon must be heated rapidly toa high temperature in the arc discharge region where it is decomposed soas to be ejected as a plasma jet which strikes the metal plate 1 to loseenergy whereupon the carbon crystallizes as diamond. Not all of thecarbon (C) from the hydrocarbon turns into diamond at this time. Rather,a considerable amount thereof precipitates as amorphous carbon orgraphite on the metal plate 1, but when hydrogen gas (H₂) is mixed withthe hydrocarbon in the starting gas 8, the amorphous carbon or graphitenondiamond components are reduced to CH₄, C₂ H₆ or other hydrocarbonswhich are removed as gases.

Actually, however, the removal action of the H₂ gas is not complete andsuch nondiamond components are detected in most diamonds film formed bythe plasma jet CVD method. This has been a factor in reducing thehardness of diamond films.

As mentioned earlier, diamond has a high hardness of 10,000 kg/mm², soit has been recognized as a potential coating material for varioustools, but the diamond film obtained by the plasma jet CVD methodcontains amorphous carbon or graphite, resulting in insufficienthardness.

Furthermore, in the past, diamond has been used in connection with highperformance tools which utilize its hardness and as heat sinks fordevices which generate large amounts of heat such as semiconductorlasers since it has a high heat conductivity of as much as several timesthat of copper.

However, when a diamond film is formed by CVD, since the materialserving as the substrate is a material (a carburizing material such as,for example, Ni, Co, and Fe) through which carbon may permeate, thecarbon component has been dispersed in the substrate making synthesis ofa diamond film impossible. Therefore, when using a diamond film for atool or heat sink in the prior art, it has been limited to basematerials (an arm in the case of a tool and a subcarrier in the case ofa heat sink) other than carburizing materials. However, it would be veryconvenient if it was possible to form a hard film like diamond on a softmaterial like a carburizing material.

SUMMARY OF THE INVENTION

Accordingly, the objects of the present invention are to eliminate theabove-mentioned disadvantages of the prior art and to provide a methodand apparatus for vapor deposition of diamond film on an object to betreated and having superior adhesiveness with the treated object.

Another object of the present invention is to provide a diamond filmsuitable for a heat sink having superior adhesiveness with a bondingmetal without impairing the heat conductivity of the diamond.

A further object of the present invention is to provide a method forforming a flat and plain diamond film on a substrate.

A still further object of the present invention is to provide a methodfor forming a diamond film having a high hardness on a substrate.

A still further object of the present invention is to form a diamondfilm on a substrate made of carburizing material.

Other objects and advantages of the present invention will be apparentfrom the following description.

In accordance with the present invention, there is provided a method forproducing a diamond film on a surface of a substrate by chemical vapordeposition, said substrate comprising a main component. The methodcomprises forming a first layer over said substrate surface, said firstlayer comprising a mixture of said main component and a sinteringreinforcement agent for diamond; forming a second layer over said firstlayer, said second layer comprising a mixture of said reinforcementagent and diamond; and forming a diamond film over the second layer. Inaccordance with the invention, the layers and the film are all formed inthe same apparatus.

In accordance with the present invention, a diamond film is provided.The film comprises (i) a diamond film formed on a metal plate bychemical vapor deposition method and (ii) a mixed phase composed ofcomponents formed from a metal capable of bonding with the diamond filmand which are included in the surface, bottom, or entirety of thediamond film.

In accordance with the present invention, there is further provided amethod of forming a diamond coating on a substrate comprisingsynthesizing a diamond film on the substrate by the CVD method using agas of a diamond forming material and a gas of a diamond nucleiformation promoter.

In accordance with the present invention, there is still furtherprovided a method for synthesis of a diamond film comprising evacuatinga reaction chamber; feeding a starting gas containing hydrogen and ahydrocarbon gas between an anode and a cathode in said evacuatedreaction chamber; causing generation of a plasma jet by arc dischargebetween said anode and said cathode; feeding a powder of tungsten,molybdenum, silicon or titanium into said plasma jet; and causing saidplasma jet to impinge on a substrate surface to thereby form a diamondfilm containing hard carbides on said surface.

In accordance with the present invention, there is still furtherprovided a method for synthesizing a diamond film comprising the stepsof forming a protective film of a carburizing material on a substrate byplasma injection using a component capable of forming a carbide having ahigh melting point; and forming a diamond film over the protective filmusing plasma chemical vapor deposition.

In accordance with the present invention, there is still furtherprovided an apparatus for effecting the formation of a diamond film onan object to be treated or on a substrate. The apparatus comprises:

an electrode forming member having a first polarity comprising anenclosed body having a nozzle opening therein for jetting thermal plasmaand a discharge gas feed pipe;

an electrode forming member having an opposite polarity and positionedin opposed relationship to said nozzle opening of said enclosed body;

a direct current plasma torch having a power source supply systemcontaining a direct current source for applying a direct current voltagebetween said electrode of first polarity and said electrode of oppositepolarity and which includes means for feeding a gas through saiddischarge gas feed pipe between the electrodes to which the directcurrent voltage is applied, forming said gas into a thermal plasma bythe direct current arc discharge between the electrodes and jetting thethermal plasma formed as a plasma jet through said nozzle;

a starting gas feeding system for feeding gaseous starting compounds forvapor phase deposition to said plasma torch;

a powder supply pipe for feeding a metal powder to said arc discharge;and

a substrate supporting mechanism for supporting the substrate in anon-equilibrium plasma and permitting a thermal plasma chemical vapordeposition film to be deposited in a vapor phase on said substrate.

In accordance with the present invention, there is still furtherprovided a method of producing a diamond film on an object to be treatedon a substrate by a chemical vapor deposition method wherein a firstlayer is formed by feeding a powder comprising a mixture of a maincomponent of the object and a sintering reinforcement agent into aplasma jet generated by direct current arc discharge, a second layer isformed by feeding a powder comprising said agent into a plasma jet, adiamond film is formed by feeding a starting gas containing hydrogen anda carbon source between an anode and a cathode of a thermal plasmachemical vapor deposition apparatus to generate a plasma jet including aradicalized carbon compound, and a surface of the object is inclined atan angle of 30 to 60 degrees from the flow direction of the plasma jetand rotated whereby the diamond film is deposited firmly on side facesof the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from the description setforth below with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view which illustrates the principles of a knownapparatus for use in the formation of a diamond film on a substrate;

FIG. 2A is a perspective view of a cooling structure of the prior art;

FIG. 2B is a sectional view of a heat sink of the prior art;

FIG. 3 is a schematic view which illustrates the principles of thepresent invention for use in the formation of a diamond film on anobject or substrate;

FIG. 4 is a sectional view for explaining the present invention;

FIG. 5 is a sectional view of a heat sink using the present invention;

FIG. 6 is a diagram illustrating an X-ray diffraction pattern of asecond intermediate layer;

FIG. 7 is a diagram illustrating the Raman spectrum of Example 4;

FIG. 8 is a diagram illustrating an X-ray diffraction pattern in thecase of a substrate having a protective film of the present invention;

FIG. 9 is a diagram illustrating an X-ray diffraction pattern in thecase of a substrate not having a protective film;

FIG. 10 is a schematic view of an apparatus for coating a diamond filmaccording to the present invention;

FIG. 11 is a cross-sectional view of an end portion of a substratecoated according to a prior art method; and

FIG. 12 is a cross-sectional view of the end portion of a substratecoated according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to a first embodiment of the present invention, a method isprovided for raising the adhesiveness between a treated object and adiamond film using a CVD apparatus for forming the diamond film and twoor more intermediate layers on the treated object, i.e., the resultantarticle comprises a first intermediate layer/second intermediatelayer/diamond film or a first intermediate layer/second intermediatelayer/third intermediate layer/diamond film.

The operation of the present apparatus will now be briefly explained.

An object (for example, a tool) to be treated or substrate is placed ona substrate holder 3 cooled by cooling water 2. At the top of thereaction chamber 4 is an anode 6 and a cathode 7 for forming a plasmajet 5. A starting gas 8 is supplied between the anode and the cathode.To enable formation of a metal layer, a powder feed pipe 9 opens at thetip of the anode 6. A DC power source 10 is provided connecting theanode 6 and the cathode 7. At the bottom of the reaction chamber 4 is anexhaust outlet 11. For CVD growth of diamond, a mixed gas of hydrogen(H₂) and a hydrocarbon, for example, methane (CH₄) is supplied betweenthe anode 6 and cathode 7 and directed into the inside of the reactionchamber 4. The exhaust system is operated for exhausting chamber 4 viaexhaust outlet 11 and thus the inside of the reaction chamber 4 is heldat a low vacuum, in which state an arc discharge 12 is caused betweenthe anode 6 and cathode 7, the heat of which causes decomposition andplasmatization of the starting gas 8, whereupon the plasma jet 5including carbon plasma strikes the metal plate 1 and a diamond film 13composed of fine crystals is grown on the metal plate 1. According tothe present invention, to grow a mixed film of metal and diamond, ametal powder is supplied through the powder feed pipe 9 into the arcdischarge 12, and to grow just a metal film, H₂ is used as the startinggas 8 and metal powder or inorganic material powder (e.g., silicon) issupplied through the powder feed pipe 9 into the arc discharge 12.

FIG. 4 is a sectional view for explaining the present invention. In FIG.4, the treated object 21 is a sintered body comprising WC or Mo₂ C, inwhich sintered body is dispersed a sintering reinforcement 23 such ascobalt (Co). In accordance with the present invention, firstintermediate layer 24 is composed of a mixture comprising, for example,90 to 99.9 wt % of the main component material of the treated object 1,i.e., WC or MoC, and 0.1 to 10 wt % of the component elements of adiamond sintering reinforcement agent, i.e., cobalt (Co), iron (Fe),nickel (Ni), or some other transition metal. The second intermediatelayer 25 is composed of a mixture comprising, for example, 0.1 to 10 wt% of the component elements of the diamond sintering reinforcementagent, i.e., cobalt (Co), iron (Fe), nickel (Ni), or other transitionmetal and 90 to 99.9 wt % diamond. The diamond film 22 is grown on thesecond intermediate layer 25.

Furthermore, according to the preferred embodiment of the presentinvention, three intermediate layers are included. The layers include afirst intermediate layer composed, for example, of 90 to 99.9 wt % of acomponent element of the object and 0.1 to 10 wt % of a componentelement of a sintering reinforcement agent for diamond, a secondintermediate layer composed of a mixture of the object component, thesintering reinforcement agent and diamond, wherein the mixture includes,for example, 0.1 to 10 wt % of the sintering reinforcement agent and 90to 99.9 wt % of the other two ingredients, and wherein the ratio of theobject component to diamond ranges from 1:9 to 9:1, and a thirdintermediate layer composed, for example, of 0.1 to 10 wt % of acomponent element of the sintering reinforcement agent and 90 to 99.9 wt% diamond.

The present invention, by providing at least two intermediate layers inthis way, and gradually changing the composition of the layers, providesan article having a diamond film 22 which is free from peeling even whenformed to a thickness of about 100 μm.

Although there are no critical limitations relative to the thickness ofthe intermediate layers and of the diamond film, the preferablethickness of each intermediate layer is 2 to 10 μm and more preferably 4to 8 μm, and the preferable thickness of the diamond film is 10 to 100μm and more preferably 20 to 40 μm. Furthermore, the size of the powderis preferably 0.1 to 8 μm, more preferably 0.4 to 1 μm.

According to a second embodiment of the present invention, the surface,bottom, or entirety of a diamond film formed by a plasma jet chemicalvapor deposition method includes a mixed phase comprised of componentmetallic elements capable of bonding with said diamond film.

The present invention uses the above-mentioned CVD apparatus to form amixed phase of diamond and a bonding metal element at the surface orbottom of the diamond film or throughout the entirety thereof.

FIG. 5 is a sectional structural view of a diamond film for use as aheat sink of a semiconductor device, wherein a mixed phase 29 of diamondand Cu is formed at the bottom surface and the top surface of thediamond film 26. The film 26 may be used in place of the film 15 of FIG.2A, for example, with the surface 27 in contact with the subcarrier 14made of Cu and with the surface 28 contacting the semiconductor chip 16.

Further, for mechanical applications utilizing the hardness of diamond,it is possible to form the mixed phase only at the bottom surface whichbonds with the object or to form the entire film as a mixed phase.

The foregoing is made possible because, while the diamond film formed bya CVD method is generally polycrystalline and therefore shearing occurseasily at the crystalline interface and the crystal is relativelybrittle, since metal is interposed in the mixed phase, the mechanicalstrength is superior.

That is, when the diamond film is used as a heat conductor, the mixedphase may be just the bonded portion. Alternatively, for applicationswhere hardness is desired, the entire film may be formed of the mixedphase to eliminate shearing.

According to a third embodiment of the present invention, a flat orplain diamond film is formed on a substrate by the CVD method using astarting gas (e.g., H₂, methane) for forming the diamond and a gas of anelement for promoting formation of diamond nuclei such as a reducingmetal (e.g., Pt), a carburizing metal (e.g., Ni, Co, Fe), or a metal orsemiconductor capable of easily forming a carbide (e.g., W, Si, Mo, Ti).

In the present invention, a diamond coating is formed by simultaneouslyor alternatingly spraying the above-mentioned diamond forming startinggas and diamond nucleus promoting element gas onto the substrate by theCVD method or by constantly spraying the starting gas and intermittentlyspraying the nucleus promoting element gas. That is, in accordance withthe present invention, in the synthesis of diamond by a vapor phasesynthesis method, an element for promoting the formation of diamondnuclei is sprayed so as to generate large quantities of high densitynuclei at the same time as the synthesis of the diamond film. The growthof specific crystal particles is thus suppressed to provide a smooth orplain diamond film. Thus, the present invention forms diamond coatingsusing the foregoing materials by CVD.

According to a fourth embodiment of the present invention, a diamondfilm having a desired high hardness can be formed on a substrate byevacuating a reaction chamber using an exhaust system, and at the sametime supplying a mixture of a hydrocarbon gas and hydrogen gas betweenan anode and cathode provided in the reaction chamber. A plasma jet ofcarbon is thus generated by arc discharge and a diamond film is formedon the substrate. While the film is being formed, a powder of an elementcapable of bonding with non-diamond carbon components in said plasma jetto form hard carbides, e.g., tungsten (W), molybdenum (Mo), silicon (Si)or titanium (Ti) is added to the plasma jet.

The present invention uses a plasma jet CVD apparatus as shown in FIG. 3to form a diamond film. As the diamond film forms, a powder of amaterial capable of forming hard carbides, e.g., W, Mo, Si or Ti isadded through powder feed pipe 9 and reacted with amorphous carbon,graphite, and other nondiamond components to form hard carbides such astungsten carbide (WC, hardness of 2200 kg/mm²), molybdenum carbide (Mo₂C, hardness of 1800 kg/mm²), silicon carbide (SiC, hardness of 2300kg/mm²), titanium carbide (TiC, hardness of 300 kg/mm²), and the like.

That is to say, amorphous carbon and graphite components are more activeenergy wise than diamond, and so such components selectively bond withradicals of metal elements in the plasma state to form hard carbides.Thus, the present invention provides for the growth of diamond film by aplasma jet CVD method using a gaseous mixture of a hydrocarbon such asCH₄ and H₂ as a starting material gas, and at the same time changing thesmall amounts of nondiamond components existing in the diamondpolycrystalline layer as a result of insufficient reduction and removalby the H₂ gas into hard carbides to thus improve hardness.

According to a fifth embodiment of the present invention, a diamond filmis formed on a substrate of a carburizing material. A protective film isfirst formed on the substrate of carburizing material by plasmainjection using an element which readily forms a carbide with a highmelting point. A diamond film is then formed over the protective film byplasma CVD.

That is, the present invention enables the coating of a diamond film ona carburizing base material by a vapor phase synthesis method by firstproviding a coating film facilitating the synthesis of diamond on thesurface of the base material.

Examples of carburizing materials usable in the present invention, areFe, Ni, Co, and other metals. Further, as elements which readily form acarbide with a high melting point, use is preferably made of WC, Si, Mo,W, or other such elements. It is possible to use these materials and toperform the method of the present invention using the same apparatus, asis clear from the examples set forth below.

When forming a protective film in accordance with the method of thepresent invention, hydrogen, argon, helium, or other inert gas isintroduced into the apparatus and is converted to plasma by DC arcdischarge. An element which readily forms a carbide with a high meltingpoint is introduced through another pipe and is melted by the hightemperature generated in the plasma to thus form a protective film overthe substrate.

According to a sixth embodiment of the present invention, a diamond filmis uniformly and firmly deposited even on the side surfaces of an objector substrate as shown in FIGS. 10 to 12.

That is, when the above-mentioned intermediate layers and diamond filmsare formed on an object (or substrate) 1, the desired layers and diamondfilm are not deposited on the side faces 30 of the object because theplasma jet 5 does not sufficiently impinge on such side surfaces 30.However, according to this embodiment, during the formation of theintermediate layers and the diamond film, the object 1 is inclined fromthe flow direction line of the plasma jet 5 by 30 to 60 degrees (See θin FIG. 10), and the object is rotated, whereby the intermediate layersand the diamond film are uniformly and firmly deposited on the sidefaces 30 of the object 1.

According to the first embodiment of the present invention, for example,if the intermediate layer 39 and the diamond film 40 are to be depositedon the side surfaces 30 of the object 1, the side surfaces 30 are notwell covered by the intermediate layer 39 because the plasma jet 5 doesnot impinge on the side surfaces 30. Accordingly, the diamond film 40may sometimes be deposited directly on the side surfaces 39 as shown inFIG. 11. Thus, the diamond film 40 on the side surfaces 30 tends to beeasily peeled off, or cracks may sometimes occur between theintermediate layer 30 and the diamond film 40, especially at the endportions of the object 1.

Contrary to the above, since the object 1 is rotated at an angle θrelative to the flow direction of the plasma jet 5 according to thisembodiment, the side faces 30 of the object 1 can be uniformly andfirmly covered with the intermediate layers 44 (39) and the diamond film40, as shown in FIG. 12. In FIG. 12, a first intermediate layer 41having a thickness of, for example, 2-5 μm is formed by introducing apowder of, for example, WC (the same material as the object), into aplasma jet 5 formed from hydrogen gas or an inert gas. A secondintermediate layer 42 having a thickness of, for example, 10-20 μm isthen formed by introducing a powder of WC and a powder of, for example,Fe, Co, Ni, Nb and/or Ta, into a plasma jet 5 generated from hydrogengas and a carbon source. A third intermediate layer 43 having athickness of, for example, 20-30 μm is formed by introducing a powderof, for example, Fe, Co, Ni, Nb and/or Ta (the same metal used in theformation of the second intermediate layer 42) into a plasma jet 5generated from hydrogen gas and a carbon source (e.g., a hydrocarbon gassuch as methane). Thereafter, a diamond film 40 having a thickness of,for example, 30-50 μm is formed in the same manner as mentioned above.

The inclination and rotation of the object (or substrate) 1 can beeffected in any conventional manner. For example, as shown in FIG. 10,the supporting means 31 for the object (or substrate) 1 is composed of acooled support 32 for the object 1, a motor 34 provided with a rotatingshaft 33 for rotating the support 32, a movable base 35 for carrying themotor 34, and an arc-shaped guide member 36 for moving the movable base35 so that the surface of object 1 to be coated is inclined at an angleθ. Although, in the above embodiment, the object 1 is moved so that itis inclined from the plasma jet flow direction, the plasma torch couldalso be moved in a similar manner.

EXAMPLES

The present invention will now be explained, in detail, by reference tobut without limitation by the following Examples.

Example 1

As the treated object 1, a sintered body using Co as a sinteringreinforcement and having a composition of WC-10% Co was used. As thecomponent materials for the first intermediate layer 24, WC and Co wereused. Further, as the component materials for the second intermediatelayer 25, diamond and Co were used. As the conditions for growth of thesecond intermediate layer and of the diamond film, the CVD apparatusshown in FIG. 3 was used and H₂ gas at 10 to 50 liter/min and CH₄ gas at0.05 to 1 liter/min were supplied to the apparatus. Further, an arccurrent of 10 to 70 A and an arc voltage variable in a range of 50 to150 V were used. The vacuum of the reaction chamber was held in therange of 1 to 10 kPa.

When growing the first intermediate layer on the treated object, H₂ gaswas supplied as the starting gas and a plasma get was generated, inwhich state WC and Co particles having a particle size of 1 to 5 μm weresupplied from the powder feed pipe 9 at a rate of 0.01 to 0.1 cc/h andplasmatized so as to grow as a deposited mixture to a thickness of 20μm.

The material gas was changed to a mixed gas of H₂ and CH₄ and a Copowder having a particle size of 1 to 5 μm was supplied from the powderfeed pipe 9 to create a plasma jet and form a second intermediate layercomprised of a mixture of diamond and Co which was deposited to athickness of 30 μm.

FIG. 6 is an X-ray diffraction pattern of the second intermediate layer,where the diffraction lines of diamond (abbreviated as D) and Co clearlyappear, so it is understood that a mixed layer was grown. Then, a plasmajet was created using a mixed gas of H₂ and CH₄ as a material gas and adiamond film having a thickness of about 100 μm was formed on top of thesecond intermediate layer top. The adhesion between the treated objectand the diamond film formed in this way is strong. A tensile test gave avalue of more than 600 kg/mm².

Example 2

The CVD apparatus shown in FIG. 3 was used and a starting gas 8 composedof hydrogen (H₂) gas at a variable flow rate of from 10 to 50 liter/minand methane gas (CH₄) at a variable flow rate of from 0.05 to 1liter/min was supplied. Further, metallic powder comprised of Cu powderwith a particle size of 1 to 5 μm was supplied through powder feed pipe9 at a variable rate of from 0.01 to 0.1 cc/h.

When use is made of a mixture of CH₄ and H₂ as the starting gas 8, adiamond film 13 is formed, and when metal particles are mixed in, amixed phase of diamond and metal is formed. Further, when H₂ gas and ametal powder are used, a metal film is formed. The conditions forcausing CVD growth are a vacuum in the reaction chamber 4 of 1 to 10kPa, an arc current of 10 to 70 A, and an arc voltage of 50 to 150 V.Thus, a diamond film having a thickness of 50 μm was formed so as toinclude a mixed phase containing Cu and having a thickness of 1 μm witha ratio of composition of the top surface and bottom surface of about5:1. Then, using this diamond film as a heat sink and using solder witha melting point of 250° C. to bond the film to a subcarrier and to alaser diode on top of it, it was possible to obtain a sufficient bondingstrength.

Example 3

In an apparatus as shown in FIG. 3, hydrogen gas, methane gas, or otherstarting gas 8 is introduced from the top of the plasma torch in thereaction chamber and is made into plasma by DC arc discharge. The plasma5 reacts on the substrate 1 to form a diamond film 13. In the process ofsynthesis, metal particulates may be introduced along with the materialgas and metal vapor sprayed on the diamond surface. In the working ofthe present invention, 10 to 50 liter/min of hydrogen gas, 0.05 to 1liter/min of methane gas, and a substrate of WC having a thickness of0.5 mm and a surface area of 10×10 mm² were used. As the spraying powdermaterial, 0.001 to 0.0001 cc of 1 to 5 μm particulates of W are suppliedeach time the thickness of the diamond film increases 0.1 mm. The arccurrent is 10 to 70 A and the arc discharge is 50 to 150 V. Further, thedegree of vacuum in the reaction chamber is 1 to 10 kPa. As a result,even with a diamond film having a thickness of 2 mm, the surfaceroughness is less than 0.05 mm.

Diamond films were synthesized under the same synthesis conditions butwith different types of metal particulates and the surface roughnesswere measured. The results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                   Pt       W        Mo                                               ______________________________________                                        Particle size (μm)                                                                      1-2        0.45-1.0 0.7-1.0                                      Arc discharge (A)                                                                          10-40      30-70    30-70                                        Diamond film 0.3 mm     0.05 mm  0.05 mm                                      roughness    or less    or less  or less                                      ______________________________________                                    

Example 4

The CVD apparatus shown in FIG. 3 was used and a super hard alloy of Wincluding 8% Co was utilized as the metal plate 1. As the conditions forthe supply of starting gas 8, the flow of hydrogen (H₂) gas was variedwithin the range of 10 to 50 liter/min and the flow of methane (CH₄) gaswas varied within the range of 0.05 to 1 liter/min and, as a metalpowder, a powder of W having a particle size of 1 to 5 μm was suppliedat a rate of 0.01 to 0.1 cc/h. Then, the conditions where CVD waspossible included a vacuum in the reaction chamber 4 of 1 kPa to 10 kPa,an arc current of 10 to 70 A, and an arc voltage of 50 to 150 V.

FIG. 7 compares the Raman spectrum 30 of a film obtained by supplying Was an additive with the Raman spectrum 31 of a film with no additive. Aswill be understood from FIG. 7, a broad peak amorphous carbon wasobserved near 1500 cm⁻¹ in the spectrum 31 of the film with no additive.

On the other hand, a sharp peak of diamond was observed at 1333 cm⁻¹ inthe spectrum 30 of the film obtained by supplying W, and the peak of theamorphous carbon near 1500 cm⁻¹ was extremely low.

It was confirmed from the Raman scattering that the diamond filmsynthesized in this way had an extremely small content of nondiamondcomponents.

Further, the hardness of the diamond film formed in this way is about10,000 kg/mm², a hardness which is close to that of natural diamond.

It is to be noted that when a Mo, Si, or Ti metal powder is suppliedfrom the powder feed pipe 9 to form a carbide, the conditions forformation of the diamond film are the same and it is possible to obtaina diamond film having a hardness that is similar to the hardnessobtained in a case where WC is formed.

In an apparatus as shown in FIG. 3, use was made of a substrate 1 of Nihaving a thickness of 0.5 mm and an inert gas (or hydrogen) wasintroduced into the plasma torch in the reaction chamber 4 at a flowrate of 10 to 50 liter/min. Then, using an arc current of 10 to 70 A andan arc voltage of 50 to 150 V, the inert gas was subjected to arcdischarge and converted to plasma. The vacuum in the reaction chamberwas 1 to 10 kPa.

As this plasmatization of the inert gas occurred, WC particulates of 1to 5 μm were supplied from a powder feed apparatus at a rate of 0.01 to0.1 cc/h. The WC particulates were melted by the high temperature plasmaand together with the plasma jet 5 were deposited on the substrate 1 toform a protective film.

Then, the supply of powder from the powder feed pipe 9 was stopped and astarting gas for forming diamond (methane and hydrogen) was introducedinto the reaction chamber 4. The feeding flow rates of the methane gasand hydrogen gas were respectively 0.05 to 1 liter/min and 10 liter/minto 100 liter/min. The starting gas was converted to plasma by the DC arcdischarge 12 at the same time and the plasma jet 5 was directed onto theprotective film to form the diamond film 13. The diamond film obtainedby the method of the present invention was subjected to X-ray analysisand the resultant pattern is shown in FIG. 8. The pattern includes apattern of a protective film and a pattern of diamond and it can be seenthat a diamond film was definitely synthesized.

On the other hand, X-ray analysis was performed on a substrate wheresynthesis of diamond was attempted without a protective film and theresultant pattern is shown in FIG. 9. As is clear from FIG. 9, only thepattern of the Ni substrate is observed and there is no diamond pattern.Thus, it was confirmed that no diamond film was synthesized.

According to the present invention, a diamond film having superioradhesiveness can be coated on a treated object, so it is possible toprovide a highly reliable diamond tool.

According to the present invention, by using a CVD apparatus which canform a mixed phase of a diamond film and metal by CVD growth and bychanging the combination of the type of starting gas and metal powder,the present invention may be employed to synthesize a diamond filmwherein the surface, bottom, or entirety of the diamond film includes amixed phase and it is therefore possible to obtain a diamond film havingsuperior adhesiveness at a low cost.

Furthermore, the method of the present invention, as explained above,uses a gas of a predetermined material to form a diamond film by the CVDmethod, so that is possible to considerably improve the smoothness ofthe surface of thickness diamond films, reduce working costs, andincrease work efficiency.

According to the present invention, a diamond film having reducedcontamination by amorphous carbon, graphite, or other nondiamondcomponents may be readily synthesized, and by working the invention itis possible to provide diamond tools at low cost.

As explained above, the present invention provides for the formation ofa protective film of a predetermined material on a substrate and thesubsequent synthesis of a diamond film on the protective film aprocedure which enables coating of a diamond film on a carburizing basematerial, which was previously impossible.

We claim:
 1. A plasma jet CVD apparatus for forming a diamond film on anobject to be treated comprising:an electrode forming member having afirst polarity comprising an enclosed body having a nozzle for jettingthermal plasma opened therein and a discharge gas feed pipe; anelectrode forming member having an opposite polarity and positioned tobe opposed to said nozzle internally of said enclosed body; a directcurrent plasma torch having a power source supply system containing adirect current source for applying a direct current voltage between saidelectrode of the first polarity and said electrode of the oppositepolarity, which feeds a gas through said discharge gas feed pipe betweenthe electrodes to which the direct current voltage is applied,generating a thermal plasma from said gas by a direct current arcdischarge between the electrodes and jetting the thermal plasma formedas a plasma jet through said nozzle; a starting gas feed system forfeeding gaseous starting compounds for vapor phase deposition to saidplasma jet; a powder supplying pipe for feeding a metal powder to an arcdischarge portion between the electrodes; and a substrate supportmechanism for supporting a substrate in a non-equilibrium plasma andpermitting a thermal plasma chemical vapor deposition diamond film to bedeposited in a vapor phase on said substrate, said support mechanismcomprising a cooled support platform for the substrate, a motor having arotatable shaft operably coupled with said support platform for rotatingthe latter, said support platform being mounted on said shaft, a movablebase carrying said motor, and a guide member mounting said movable basefor movement so that the substrate on the platform is positioned with asubstrate surface thereof to be coated inclined at an angle θ relativeto said plasma jet.